The Firn Air Content of Larsen Ice Shelf

A method is presented for using ice sounding measurements to decompose the total thickness of any given ice shelf into a solid-ice thickness and a dry-firn air thickness (or saturated-firn water thickness). The method is applied to data from the 1997/98 British-Argentine airborne radar survey of Larsen Ice Shelf, revealing large spatial gradients in dry-firn air thickness that are consistent with existing measurements and atmospheric modelling. The spatial variation of firn air thickness appears to correlate well with the pre-1998 annual mean distribution of cumulative melt days. This provides some insight into whether a loss of firn air could account for the satellite-observed surface lowering of Larsen Ice Shelf.